In recent years, packaging becomes the performance-limiting factor for microelectronic device, and the issues such as size, weight, cost, pin count, and power consumption are important for packaging design. More particularly, the concern of heat dissipation becomes more important when the power and operation frequency of electronic systems increase.
The nowadays heat-dissipation means for semiconductor package can be classified to following three types:
(1) Heat sink is generally metal plate set arranged externally to the package of the semiconductor. PA0 (2) Heat spreader is metal plate encapsulated within the package and functions to convey the thermal energy from chip to environment. PA0 (3) Heat slug is also arranged within the package but portion thereof exposes to outside.
In above-mentioned heat-dissipation means for semiconductor package, the heat spreader and heat slug have more profound effect on the semiconductor package because they are entirely or largely placed within the molding compound of the package. As to heat slug, gap is liable to form on the junction of molding compound and heat slug, because the slug has partial portion exposing outside. The moisture might be entrapped from the gap and accumulated within the package. The semiconductor package has the risk of cracking (popcorning) when subjected to a following soldering process due to the thermal expansion of moisture.
As to the heat spreaders, they do not suffer to the problem mentioned above because they are entirely enclosed within the package. However, when the heat spreader is arranged below the paddle, gap is liable to form between the paddle and the heat spreader because the heat spreader is thin and hard to attach to the paddle closely. The gap is also tends to accumulate moisture and induce the problem of popcorning.
FIG. 1, FIG. 2A, FIG. 2B show the perspective view, top view and cross section view of a conventional heat spreader, respectively. As can be seen from those figures, the conventional heat spreader is generally a metal plate 10 having a plurality of lower bumps 12 and a plurality of through holes 14, wherein the through holes 14 are provided to facilitate the filling of the molding compound. FIG. 3 shows the arrangement of the aforementioned heat spreader within a semiconductor package. As can be seen from this figure, the chip 15 is bonded to the paddle 16 by viscous adhesives (not shown) such as silver epoxy. Then the heat spreader 10 is attached below the paddle 16 and the resulting structure is encapsulated with a molding compound 17 to complete the package. However, because the heat spreader 10 and the paddle 16 are generally thin-sheet form, they are hard to attach closely. Therefore, gap or delamination is liable to entrap moisture. The semiconductor package has the risk of popcorning when subjected to a following soldering process due to the thermal expansion of moisture.